1975 911S stalls

[bvegas21]

I bought this car a few months ago and I'm really not mechanically inclined yet. The alternator went out and I had it replaced. On the drive home I noticed that when I applied the brake the alternator light came on the dash and the car would stall. On the freeway I'm fine, but when stopping at lights the car dies. Please help, is it the Idle speed (car idles very low and stalls if I don't keep foot on gas)? If so any advice on how to adjust this? Or is there another problem I need to look into? I have the original manual for the car and it says when that alternator light comes on its either the alternator, V-belt, or ... something else I can't think of right now.
Any advice would be greatly appreciated as I don't feel comfortable taking the car back to the guys who did the repairs.

[Paulporsche]

Welcome.

There may be a number of things at play here. Among the more common are your idle speed adjustment, your mixture adjustment, and your points. It's possible your idle speed is simply set too low or your mixture is set too rich, but it could also be something more serious/costly.

It's always best to establish a baseline for comparison w/ any new old car, especially one w/o electronic aids. If you have a mechanic you trust, have him do a tuneup, incl points, plugs, rotor, wires, timing, and setting your CO to about 3.5%.

If you want to do this yourself, search the archives for Jim Williams' site , which has lots of info on the CIS fuel injection. Member Souk and others have also contributed much on the adjustment and care of this system. Also the Bentley manual for SC models has quite a bit of info that applies to your car.

Tell us more about your symptoms. How does the car start and idle during warmup? Does this stalling happen when cold or warm, or both? Where are you located?

Also, it's tradition to post a pic of your car.

[bvegas21]

I purchased the car in December '05. Back in December I had a mechanic "lean" it out to get the car to pass smog. It ran well for about a month or two. Then it sat for a month and wouldn't start. I'd jump the battery but it wouldn't hold a charge. So I saved some money and took it in (a motorcycle mechanic friend suggested it was the alternator). The shop called and said the alternator was the problem so they replaced it. I just got it back yesterday. The drive on the freeway was fine. As soon as I got off the freeway I was braking and the car died. Then it was like that all the way home. Every stop light the car would die. The engine turns over fine, initially when idling the car will die, after a minute or two then its fine. I just ran over to my parents house (that's where I have it stored) and took it for a spin. For the first 10 minutes there were no problems, car ran fine, did not die. Then I took it to get gas. Once I pulled into the gas station and put the car in neutral and pressed the brake the car died. Also, that damn alternator light came on (its the bottom light on the "Temp" and "Press" gauge) just as it had yesterday when I came off the freeway. Riding back from the gas station I downshifted to 2nd gear and the car felt like it was going to die so I gave it some gas and let up on the clutch and after some hesitation it jumped into gear. I looked at the original owner's manual which was still int he car and it said that when the "alternator warning light" comes on it may be the alternator, the V-belt, or the regulator. Hopes this information is more useful, as I've said I'm not a mechanic I'm leaving as I go here.
Attached is a photo.
Thanks

[kpfoten]

Does it charge on idle? If the charging system is up to par, then I would pull the CIS and replace all hoses, including intake runner boots, etc. See a recent thread--I just had a problem with stalling when I would push my clutch in. Changed all the rubber and now I've got a new car.

[Paulporsche]

Check to see what type of CDI box you have. If you have a Permatune (especially a silver one) you may have what seems to be a very common problem in that they fail after they get hot.

Where do you live that requires a 75 to pass a smog test?

[bvegas21]

I live in Las Vegas, Nevada. It's been in the 100 degrees here lately. The charging system should be up to par, I just had the alternator replaced last week and just picked up the car from the shop on Saturday. There's almost no Porsche mechanics here in town. Only two guys and a dealership that sells 'em new. I have the Haynes manual and the Dempsy book - 101 Projects for your Porsche 911. I'll see if those can help me track down what and where the hell the CDI box and CIS is. Is the CDI box mounted to the left side of the engine compartment? If so then it is silver. The most I've ever done mechanically is change the clutch on my old '66 Volvo P1800. Seriously, I'm pretty clueless.

[ossiblue]

If the alternator has been replaced, the warning light coming on is most likely a function of the low rpm's as the engine starts to die. I know this isn't much help given what you've told us about the mechanic situation, but your best bet is to hunt up a 911 expert to get the base line set for performance. There are so many possibilities for the cause of your problem and an experienced mechanic is the best way to go. Good luck, and keeep us posted.

[Paulporsche]

If I HAD to guess, I would say your mixture is still too rich or your points are bad. However, as stated before, there could be many other reasons. It sounds like you are new to these cars (Isn't everyone @ first?) so I would recommend you use the search function to find out all you can about your symptoms. Also, the Bentley manual is a lot better than the Haynes, even if it is for the SC. And finally, as I said previously, see if you can find some mechanic who can at least verify that the car is OK re mixture, ignition and timing.

[sketchers356]

Im still thinking that it is the idle. If the car is idling really low then the alternator light will go on as the alternator is not putting out enough volts. Are there only issues when the car is idling?

[Paulporsche]

What is your normal idle speed?

[RoninLB]

adjust warm idle to 1,000 rpm and see what happens.